Voxel raymarching now with fragment shading rate

Here is the mask (if you will) of shading rates I'm using:

Red corresponds to a 1x1 to 1x1 fragment shading rate, green is 1x1 to 2x2, and blue is 1x1 to 4x4

This feature with be adjustable and will be by default set to off.  On 4k monitors, this may be very useful for better rendering performance without a huge sacrifice in visual quality.

This explains what fragment shading rate is and why it's useful: https://docs.vulkan.org/samples/latest/samples/extensions/fragment_shading_rate_dynamic/README.html

Note that I am not using dynamic shading rate.